1. Field of the Invention
The present invention relates to a refrigerating apparatus having a defrosting capability for use in a compartment.
2. Description of the Prior Art
A refrigerant circuit diagram of a refrigerating apparatus in the prior art is shown in FIG. 3. In this figure, reference numeral 1 designates a compressor, numeral 2 designates a condensor, numeral 3 designates a throttle, numeral 4 designates an evaporator, numeral 5 designates a hot gas modulating valve, numeral 6 designates a condensor fan, numeral 7 designates an evaporator fan, numeral 8 designates an electric heater, numeral 9 designates a return air temperature detector, numeral 10 designates an overheating preventing temperature detector, numeral 11 designates an evaporator outlet refrigerant temperature detector, and numeral 20 designates a controller.
A cross-sectional view of a compartment equipped with the above-described refrigerating apparatus is shown in FIG. 4. In this figure, reference numeral 12 designates the compartment, and a dash-line arrow therein indicates a flow of air. In this figure are shown the locations of the evaporator 4, the evaporator fan 7, the electric heater 8, the return air temperature detector 9 and the overheating preventing temperature detector 10.
In the above-described apparatus, a high-temperature high-pressure gas refrigerant compressed by the compressor 1 enters the condensor 2. Here, the refrigerant is cooled by air blown by the condensor fan 6 and becomes a liquid refrigerant; then, it is reduced in pressure by the throttle 3 and enters the evaporator 4, wherein it is heated by air blown by the evaporator fan 7, and it evaporates and returns to the compressor 1. At this time, the blown air is refrigerated in the evaporator 4 and is further blown out into the compartment to refrigerate the interior of the compartment.
The controller 20 compares a temperature detected by the return air temperature detector 9 with a set value corresponding to a predetermined temperature, adjusts a degree of opening of the throttle 3 and the hot gas modulating valve 5, selects an operating mode, and carries out a control operation for maintaining the temperature in the compartment 12 constant.
As the temperature in the compartment decreases, frost begins to adhere to the surface of the evaporator 4, whereby the operating efficiency of the evaporator also decreases. In order to recover this loss, the compressor 1, the evaporator fan 7 and the condensor 6 are stopped, and a defrosting mode of the evaporator 4 is effected by feeding an electric current to the electric heater 8. The timing for effecting the defrosting mode is T.sub.1 minutes after the start of operation of the refrigerating apparatus or after the completion of the last defrosting cycle. Defrosting is also carried out when a temperature TE detected by the evaporator outlet refrigerant temperature detector 11 has become lower than a set value STE1. Also, the defrosting mode is ceased when a temperature TE detected by the evaporator outlet refrigerant temperature detector 11 has become higher than a set value STE2 or T.sub.2 minutes have elapsed after the commencement of the defrosting mode.
When anomalies occur in the evaporator outlet refrigerant temperature detector 11, for instance, when defrosting is effected and even though the detection temperature TE is not indicated by the aforementioned detector 11 as having risen higher than the set value STE2, naturally the defrosting is forcibly finished nonetheless according to the set value T.sub.2 of the timer. Therefore, in the event that only a little frost has accumulated, the timer set value T.sub.2 is too long and the temperature in the container rises excessively, sometimes resulting in damage of the cargo in the compartment. Also, contrary to the above-described case, under some circumstances the apparatus does not effect the defrosting mode even though frost has accumulated to a significant degree; hence, frost adheres excessively to the evaporator and the operating efficiency thereof deteriorates.